Merge branch 'pw/rebase-keep-base-fixes' into pw/rebase-reflog-fixes

* pw/rebase-keep-base-fixes: rebase --keep-base: imply --no-fork-point rebase --keep-base: imply --reapply-cherry-picks rebase: factor out branch_base calculation rebase: rename merge_base to branch_base rebase: store orig_head as a commit rebase: be stricter when reading state files containing oids t3416: set $EDITOR in subshell t3416: tighten two tests